Imaginary-Time Matrix Product State Impurity Solver for Dynamical Mean-Field Theory

We present a new impurity solver for dynamical mean-field theory based on imaginary-time evolution of matrix product states. This converges the self-consistency loop on the imaginary-frequency axis and obtains real-frequency information in a final real-time evolution. Relative to computations on the real-frequency axis, required bath sizes are much smaller and no entanglement is generated, so much larger systems can be studied. The power of the method is demonstrated by solutions of a three-band model in the single- and two-site dynamical mean-field approximation. Technical issues are discussed, including details of the method, efficiency as compared to other matrix-product-state-based impurity solvers, bath construction and its relation to real-frequency computations and the analytic continuation problem of quantum Monte Carlo methods, the choice of basis in dynamical cluster approximation, and perspectives for off-diagonal hybridization functions.